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    SubjectRe: [PATCH 5/7] Fix not good check of mem_cgroup_local_usage()
    On Thu 16-06-11 12:54:43, KAMEZAWA Hiroyuki wrote:
    > From fcfc6ee9847b0b2571cd6e9847572d7c70e1e2b2 Mon Sep 17 00:00:00 2001
    > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > Date: Thu, 16 Jun 2011 09:23:54 +0900
    > Subject: [PATCH 5/7] Fix not good check of mem_cgroup_local_usage()
    >
    > Now, mem_cgroup_local_usage(memcg) is used as hint for scanning memory
    > cgroup hierarchy. If it returns true, the memcg has some reclaimable memory.
    >
    > But this function doesn't take care of
    > - unevictable pages
    > - anon pages on swapless system.
    >
    > This patch fixes the function to use LRU information.
    > For NUMA, for avoid scanning, numa scan bitmap is used. If it's
    > empty, some more precise check will be done.
    >
    > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > ---
    > mm/memcontrol.c | 43 +++++++++++++++++++++++++++++++++----------
    > 1 files changed, 33 insertions(+), 10 deletions(-)
    >
    > Index: mmotm-0615/mm/memcontrol.c
    > ===================================================================
    > --- mmotm-0615.orig/mm/memcontrol.c
    > +++ mmotm-0615/mm/memcontrol.c
    > @@ -632,15 +632,6 @@ static long mem_cgroup_read_stat(struct
    > return val;
    > }
    >
    > -static long mem_cgroup_local_usage(struct mem_cgroup *mem)
    > -{
    > - long ret;
    > -
    > - ret = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_RSS);
    > - ret += mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_CACHE);
    > - return ret;
    > -}
    > -
    > static void mem_cgroup_swap_statistics(struct mem_cgroup *mem,
    > bool charge)
    > {
    > @@ -1713,6 +1704,23 @@ static void mem_cgroup_numascan_init(str
    > mutex_init(&mem->numascan_mutex);
    > }
    >
    > +static bool mem_cgroup_reclaimable(struct mem_cgroup *mem, bool noswap)
    > +{
    > + if (!nodes_empty(mem->scan_nodes))
    > + return true;

    How the non empty node mask guarantees that there is some reclaimable memory?

    > + /* slow path */
    > + if (mem_cgroup_get_local_zonestat(mem, LRU_INACTIVE_FILE))
    > + return true;
    > + if (mem_cgroup_get_local_zonestat(mem, LRU_ACTIVE_FILE))
    > + return true;
    > + if (noswap || !total_swap_pages)
    > + return false;
    > + if (mem_cgroup_get_local_zonestat(mem, LRU_INACTIVE_ANON))
    > + return true;
    > + if (mem_cgroup_get_local_zonestat(mem, LRU_ACTIVE_ANON))
    > + return true;
    > + return false;
    > +}
    > #else
    > int mem_cgroup_select_victim_node(struct mem_cgroup *mem)
    > {
    > @@ -1722,6 +1730,21 @@ static void mem_cgroup_numascan_init(str
    > {
    > return 0;
    > }
    > +
    > +static bool mem_cgroup_reclaimable(struct mem_cgroup *mem, bool noswap)
    > +{
    > + if (mem_cgroup_get_zonestat_node(mem, 0, LRU_INACTIVE_FILE))
    > + return true;
    > + if (mem_cgroup_get_zonestat_node(mem, 0, LRU_ACTIVE_FILE))
    > + return true;
    > + if (noswap || !total_swap_pages)
    > + return false;
    > + if (mem_cgroup_get_zonestat_node(mem, 0, LRU_INACTIVE_ANON))
    > + return true;
    > + if (mem_cgroup_get_zonestat_node(mem, 0, LRU_ACTIVE_ANON))
    > + return true;
    > + return false;
    > +}
    > #endif

    Code duplication doesn't look good. What about a common helper?
    >
    >
    > @@ -1811,7 +1834,7 @@ again:
    >
    > while (visit--) {
    > victim = mem_cgroup_select_victim(root_mem);
    > - if (!mem_cgroup_local_usage(victim)) {
    > + if (!mem_cgroup_reclaimable(victim, noswap)) {
    > /* this cgroup's local usage == 0 */
    > css_put(&victim->css);
    > continue;
    >
    > --
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    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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